This invention relates to a four-stroke reciprocatory internal combustion engine and to a method of operating such a four-stroke reciprocatory internal combustion engine.
The permissible limits of exhaust emissions in certain countries such as Japan are shown in the following tabulation:
______________________________________ HC CO NOx g/mile g/mile g/mile ______________________________________ 1978 standard (Japan) 0.40 3.36 0.40 ______________________________________
Car manufactures are now striving hard to develop a fuel economy engine which meets the above stringent standard.
In present spark ignition internal combustion engines under idle and deceleration conditions the air fuel ratio (A/F) of the charge in the cylinder must be kept rich enough to allow the engine to run smoothly because under these conditions the rate of residual gas of the charge in the cylinder increases abruptly. Empirically it is known that the engine stability is directly affected by G/F, rather than A/F, of the charge in the cylinder, where, G=(intake air content)+(residual gas content), and that there is optimum range of G/F around which the engine runs smoothly. In practice, the A/F of the charge in the cylinder is kept excessively rich and the rate of residual gas of the charge is considerably great under idle and deceleration conditions so that the exhaust gas resulting from the combustion of the charge will contain high HC and CO under these conditions. To reduce CO and HC, it is therefore necessary to supply secondary air under idle and deceleration conditions for facilitating oxidation reaction of CO and HC in an exhaust gas treatment device.
If, under idle and deceleration conditions, the engine can run smoothly when the A/F of the charge in the cylinder is around the stoichiometry, CO and HC levels will be lowered. This, however, is not yet accomplished and its accomplishment is strongly desired for the purpose of providing a fuel economy low emission engine.
It is also desired to operate the engine, under part load conditions, on the charge whose A/F is around the stoichometry.
To attain fuel economy of a car, it is effective to reduce the volume of the cylinder. So, it is desired to increase the power output of the engine under full load conditions.